Tubes having indentations formed therein

ABSTRACT

A hollow metal tube having a sharp-angled indentation that is made without removing any material and without deforming the external diameter while conserving the fiber orientation of the metal and maintaining a constant thickness of the tube. The process of forming the sharp-angled indentation comprises the steps of, providing a riveting machine, the riveting machine having an epicycloid mechanism and a spherical joint and comprising a riveting head fitted to a spindle, operating in conjunction with pressing devices and a fixed half-clamp, replacing the spindle of riveting machine with a sharp angled former adapted to the profile of the indentation to be made and to the former&#39;s sharp angle, inserting the tube on which indentations are to be made between the former and the fixed half-clamp, and activating the pressing devices to cause movement of the spindle in order to form the sharp-angle indentation in the tube.

RELATED APPLICATIONS

[0001] This is a divisional application of U.S. Ser. No. 09/314,279filed on May 15, 1999 that claimed priority of European PatentApplication No. 98 401 857.2 filed Jul. 27, 1998.

TECHNICAL FIELD

[0002] This invention relates to a process by which it is possible tomake a sharp-angled indentation on hollow tubes without removing anymaterial, maintaining a constant thickness of tube and also withoutdeforming the external diameter and conserving the fiber orientation ofthe metal.

[0003] In many industrial fields, it is necessary to make a series ofindentations in tubes for adjustment purposes.

[0004] As a non-exhaustive illustration, such indentations are used inthe automobile industry when making “frames” for adjustable headrestraints for motor vehicles.

[0005] In order to make indentations in tubes, processes have alreadybeen proposed that involve machining and removing material, a techniquewhich is difficult to apply in the case of hollow tubes, or that use apress, which leads to deformation (caving in) of the tubes, makingfurther machining necessary, and which does not enable sharp-angledindentations to be produced.

[0006] The presence of sharp-angled indentations is essential in orderto ensure catches are properly engaged and that positions can beadjusted.

[0007] Consequently, the “frames” of head restraints for motor vehiclesare, as a general rule, currently made from non-tubular, solidcylindrical metal bars, which to a great extent increases their weightand their cost price.

OBJECTS OF THE INVENTION

[0008] The purpose of this invention is to resolve these problems byoffering a process that makes it possible to make sharp-angledindentations on hollow tubes, without removing any material.

[0009] According to this invention, it has been possible, surprisingly,to achieve this objective not by means of a press as has previously beenproposed, but by means of a riveting machine which in itself is awell-known machine, comprising a riveting head fitted to a spindleoperating in conjunction with pressing devices and a fixed half-clamp.

SUMMARY OF THE INVENTION

[0010] The process used in this invention is characterized by the factthat the riveting head of a riveting machine of this type is replaced bya former adapted to the profile of the indentation to be made and inparticular to its sharp angle. The tube on which indentations are to bemade is inserted between the former and the fixed half-clamp and thepressing devices are activated, causing movement of the spindle, inorder to allow indentations to be made in the tube.

[0011] Thus by radial deformation it is possible to obtain indentationsof various shapes, without removing any material, and to maintain asharp angle in the side engaged by the catch, without deforming theexternal diameter of the tube.

[0012] One possible characteristic of the invention is that the rivetingmachine is a riveting machine with an epicycloid mechanism and aspherical joint.

[0013] When such a machine is used, the indentation former is subjectedto a complex movement that can be broken down into a translationalmovement and an orbital movement.

[0014] It has thus been possible to make indentations in tubes with adepth one-and-a-half times their thickness, without perforating thedeformed part.

[0015] Another possible characteristic of the invention is that thespindle of the riveting machine is fitted with a holding-down clamp, thefront part of which secures the tube in which indentations are to bemade and holds it tightly against the fixed half-clamp.

[0016] Another possible characteristic of the invention is that rotationmovement of the indentation former is prevented by means of astabilizing device.

[0017] There are no limits in terms of the maximum and minimum tubediameters that can be handled by the process. The depth and the surfacearea to be obtained determine the power of the riveting machine.

[0018] By way of example, tests have been carried out on steel tubeswith an external diameter of 11.70 mm and an internal diameter of 7.80mm. A force of 500 daN was required in order to obtain indentations 2 mmin depth with an area of 50 mm².

[0019] The invention also relates to a hollow tube produced by means ofthe process described above.

[0020] Such a tube is characterized by the fact that it has sharp-angledindentations which have been made without removing material, maintainingconstant tube thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The characteristics of the process and the tubes covered by theinvention will be described in greater detail by referring to theappended drawings, in which:

[0022]FIG. 1 is a perspective view of a tube as according to theinvention;

[0023]FIG. 2 is a section through this tube;

[0024]FIG. 3 is a schematic section of the riveting machine used in thisprocess;

[0025]FIG. 3a is a schematic section of FIG. 3 along axis A-A;

[0026]FIGS. 4 and 4a, 5 and 5 a, 6 and 6 a show three examples ofindentation formers as sections and views from below, respectively.

DETAILED DESCRIPTION OF THE INVENTION

[0027] According to FIG. 1, the surface of the tube (1) has a series ofindentations (2) of a determined profile.

[0028] According to FIG. 2, the indentations (2) have sharp angles (3)and are made without removing material so that the thickness of the tuberemains constant.

[0029] According to FIG. 3, the riveting machine (4) used to makeindentations in the tubes (1) is a machine with an epicycloid mechanismand a spherical joint, which is a well-known type of machine and which,for this reason, will not be described in detail in the context of thisstatement.

[0030] This machine is equipped, firstly, with a fixed half-clamp (5)and secondly a moving half-clamp or holding-down device (6) fixed to thehead of the machine (4) by means of a screw (7) in conjunction withsleeves or springs made of rubber.

[0031] According to FIG. 3a, the two parts (5, 6) have grooves (8, 8′)located opposite each other in order to hold the tube (1) in whichindentations are to be made.

[0032] Furthermore, and as shown in FIG. 3, the machine (4) is alsofitted with a former (9) fitted to the nose of the same.

[0033]FIGS. 4, 4a, 5, 5 a, 6 and 6 a show examples of former profiles(9) which can be used according to the type of indentation to beproduced.

What is claimed is:
 1. A hollow metal tube having a sharp-angledindentation that is made without removing any material and withoutdeforming the external diameter while conserving the fiber orientationof the metal and maintaining a constant thickness of the tube, where theprocess of forming the sharp-angled indentation comprises the steps of,providing a riveting machine, the riveting machine having an epicycloidmechanism and a spherical joint and comprising a riveting head fitted toa spindle, operating in conjunction with pressing devices and a fixedhalf-clamp, replacing the spindle of riveting machine with a sharpangled former adapted to the profile of the indentation to be made andto the former's sharp angle, inserting the tube on which indentationsare to be made between the former and the fixed half-clamp, andactivating the pressing devices to cause movement of the spindle inorder to form the sharp-angle indentation in the tube.
 2. A hollow metaltube as described in claim 1 , characterized in that the spindle of theriveting machine is fitted with a holding-down clamp, the front part ofwhich secures the tube in which indentations are to be made and holds ittightly against the fixed half-clamp.
 3. A hollow metal tube asdescribed in claim 1 , characterized in that the riveting machineeffects riveting by a rotational movement and the rotational movement ofthe indentation former is prevented by means of a stabilizing device. 4.A hollow metal tube as described in claim 2 , characterized in that theriveting machine effects riveting by a rotational movement androtational movement of the indentation former is prevented by means of astabilizing device.
 5. A process for making a hollow metal tube having asharp-angled indentation formed without removing any material andwithout deforming the external diameter while conserving the fiberorientation of the metal and maintaining a constant thickness of thetube, where the sharp-angled indentation is formed by a processcomprising the steps of, providing a riveting machine, the rivetingmachine effecting riveting by a rotational movement and comprising ariveting head fitted to a spindle, operating in conjunction withpressing devices and a fixed half-clamp, replacing the spindle of theriveting machine with a sharp angled former adapted to the profile ofthe indentation to be made and the former's sharp angle, inserting thetube on which indentations are to be made between the former and thefixed half-clamp and activating the pressing devices causing movement ofthe spindle in order to allow indentations to be made in the tube andpreventing rotational movement of the indentation former by means of astabilizing device.
 6. A process for making a hollow metal tube having asharp-angled indentation formed without removing any material andwithout deforming the external diameter while conserving the fiberorientation of the metal and maintaining a constant thickness of thetube, where the sharp-angled indentation is formed by a processcomprising the steps of, providing a riveting machine, the rivetingmachine effecting riveting by a rotational movement and comprising ariveting head fitted to a spindle, operating in conjunction withpressing devices and a fixed half-clamp, replacing the spindle of theriveting machine with a sharp angled former adapted to the profile ofthe indentation to be made and the former's sharp angle, inserting thetube on which indentations are to be made between the former and thefixed half-clamp and fitting the spindle of the riveting machine with aholding-down clamp, the front part of which secures the tube in whichindentations are to be made and holds it tightly against the fixedhalf-clamp, and activating the pressing devices causing movement of thespindle in order to allow indentations to be made in the tube andpreventing rotational movement of the indentation former by means of astabilizing device.